If a workout brings on hives, it’s less likely the perspiration and more likely your own body heat that’s to blame.

On a frigid winter’s night, Lise Kavanagh doesn’t bury herself under blankets. When she wakes up to a chilly morning, she doesn’t take a hot shower. Nor will she dress in super warm clothes to head out for the day.

Is this superwoman immune to cold? Nope.

Instead, she’s hyper-sensitive to heat. In fact, when her body temperature rises, she develops an itchy rash all over her body. Kavanagh has what’s known as cholinergic urticaria or hives. Her body reacts with hives to the physical stimulus of heat.

Sometimes at the gym, you’ll hear dubious tales of a runner who’s “allergic to their own sweat”. Chances are, it’s not the perspiration – it’s the heating up of the body through exercise that’s causing the person to break out in a rash.

Cholinergic urticaria can be triggered by several heat-raising activities: jogging or aerobic workouts are obvious, but also hot baths or showers, eating spicy foods, and even emotional stress can bring on the hives.

For Kavanagh, “some of my worst attacks happen when I’m sleeping. Even if I have no blankets at all, when I stir in the night and end up on my back, the heat accumulates between the mattress and my skin, and I’ll wake up with a rash all over my back.”

While a relatively rare condition, experts say that 5 per cent of people who have chronic urticaria also experience the cholinergic symptoms. In the United States, it’s estimated that one in five people will experience chronic urticaria in their lifetime.

Spotting the Condition

With cholinergic urticaria or CU, the hives are tiny, about the size of a ball point pen tip. The rash comes on rapidly, usually within a few minutes of perspiring, and can last from 30 minutes to an hour or more before receding once the body returns to normal temperature.

The hives or “wheals” are very itchy, and can be preceded by a burning, tingling and/or warm sensation.

The wheals may join to form a large mass of swelling, and some people also experience headaches, salivation, palpitations, fainting, shortness of breath, abdominal cramps and diarrhea.

“CU appears when the affected individual’s body is heated by exertion or a situation that raises the core temperature of the body 2.7 degrees F or more,” says Dr. Martin Ostro, staff physician with the division of allergy and immunology at Massachusetts General Hospital in Boston.

Technically, it’s not an actual allergy since cholingeric urticaria has no specific IgE, the allergic antibody, created to respond to a particular substance. But the mechanism of the reaction is similar to allergy.

In patients with chronic urticaria, modest amounts of heat will cause mast cells to release histamine and other chemicals, resulting in hives and swelling. Ostro says this disruption of the mast cells, and an increased tendency for this to occur, are in fact, the underlying causes of chronic urticaria.

How to Treat?

Avoidance is the best treatment for cholinergic hives, but that may be difficult in warm weather or when exercising. “CU can usually be prevented by daily administering a long-acting, non-sedating antihistamine, such as cetirizine [Zyrtec or Reactine],” says Ostro.

If a rash does appear, it helps to cool the area promptly. “Ice cubes are the best,” says Kavanagh, “but I’m happy with cold water. Water is my best ally because wherever I am, water is fairly accessible.”